1. (a)
integral proteins are embedded in the membrane/phospholipid bilayer;
peripheral proteins are on the surface of the membrane;
some integral proteins (are transmembrane proteins that) extend from
one side of the membrane to the other;
hormone binding sites;
e.g. insulin;
enzymes;
e.g. sucrase / succinate dehydrogenase;
cell adhesion;
cell-to-cell communication recognition / antigenic markers /
glycoproteins / contact inhibition;
channels/pores for passive transport/facilitated diffusion;
pumps/carriers for active transport;
receptors for neurotransmitters;
such as acetylcholine;
electron carriers;
e.g. electron transport chain of cellular respiration;
pigments (in rods/cones); 8 max
Award any of the above points if clearly drawn in an annotated diagram.
(b) non-polar amino acids cause channel proteins to embed in a
membrane;
polar amino acids at either end cause channel proteins to be
transmembrane / retain protein position in membrane;
polar amino acids lining pore allow polar particles to pass through/
form hydrophilic channels through membranes;
polar amino acids on surface of enzyme allow it to dissolve in water;
polar and non-polar amino acids contribute to the specificity of
an enzyme;
non-polar amino acids of surface of enzyme allow it to embed
in a membrane;
polar amino acids at active site of enzyme attract polar substrates;
positively charged amino acids attract negatively charged
substrate / vice versa;
non-polar amino acids at active site attract non-polar substrate;
5 max
Award any of the above points if clearly drawn in an annotated diagram.
(c) Answers do not need to be shown in a table format. Award marks
only when there is a comparison of both types of inhibition.
Competitive inhibition
Non-competitive inhibition
substrate and inhibitor are (chemically) similar/same shape
substrate and inhibitor are (chemically) not similar/different shape;
inhibitor binds to active site
inhibitor binds away from the active site/allosteric site / diagram to illustrate difference;
inhibitor does not change the shape of the active site
inhibitor changes the shape of the active site;
increases in substrate concentration reduce the inhibition
increases in substrate concentration do not affect the inhibition / annotated graph to illustrate the difference;
both types of inhibitor reduce enzyme activity;
both types of inhibitor bind to the enzyme;
both types of inhibitor prevent the substrate from binding to the active site;
example e.g. succinate dehydrogenase is inhibited by malonate
example e.g. pyruvate kinase is inhibited by alanine;
5 max
(Plus up to [2] for quality)
[20]
2. (a)
structure — collagen;
transport—transthyretin / hemoglobin;
enzyme/catalyst — lysozyme;
movement — actin / tubulin;
hormones — insulin;
antibodies — immunoglobulin;
storage —albumin;
Accept any other valid function of proteins with a named example.
For example, sodium potassium pump, but do not accept simply “in
membranes” without a clear function.
To award [4 max], responses need a function of protein and a
named example.
Only accept the first four answers. 4 max
(b) made of protein;
made of rRNA;
large subunit and small subunit;
three tRNA binding sites;
Aminacyl/A, Peptidyl/P and Exit/E;
mRNA binding site (on small subunit);
70S in prokaryotes / 80S in eukaryotes;
can be free / bound to RER (in eukaryotes); 6 max
(c) RNA polymerase; (polymerase number is not required)
binds to a promoter on the DNA;
unwinding the DNA strands;
binding nucleoside triphosphates;
to the antisense strand of DNA;
as it moves along in a 5′→3′ direction;
using complementary pairing/A-U and C-G;
losing two phosphates to gain the required energy;
until a terminator signal is reached (in prokaryotes);
RNA detaches from the template and DNA rewinds;
RNA polymerase detaches from the DNA;
many RNA polymerases can follow each other;
introns have to be removed in eukaryotes to form mature mRNA;
8 max
(Plus up to [2] for quality)
[20]
3. (a)
The structures underlined must be labelled.
(complementary) bases labelled with at least one of each of A, G, T and C
correctly linked to C1;
hydrogen bonds between correct complementary bases;
{Bond numbers not required.
correct antiparallel orientation shown; (as seen by shape or
orientation of sugar)
4 max
(b) (eight) histone (proteins);
DNA wrapped around histones/nucleosome;
further histone holding these together;
Do not allow histone wrapped around DNA.2 max
(c) primary structure is (number and) sequence of amino acids;
joined by peptide bonds;
tertiary structure is the folding of the polypeptide/secondary
structure/alpha helix;
stabilized by disulfide/ionic/hydrogen bonds/hydrophobic
interactions;
tertiary structure gives three dimensional globular shape/shape
of active site;
3 max
[9]
4. (a)
50 – 12 = 38 (mm2); Accept 12–50 = –38
(38 ÷ 50) x 100 = (–)76%; (ECF) 2
(b) Sesamia (was most successfully controlled);
in control plants Sesamia caused most damage;
all types of Bt/genetically modified maize/A–I show (significant) decrease
in damage by Sesamia;
mark for correct numerical comparison;
Sesamia caused no damage to type E/ in one instance;
Busseola not controlled/affected by Bt/genetically modified maize/
caused largest amount of damage in types A–I/increased damage in
some varieties;
Eldana controlled by some types of maize / B/C/D but not others /
Eldana caused least damage in control and not much difference in
many maize types; 3 max
(c) males: (440 – 325 =) 115 g; (Accept answers in range 105–125 g)
females: (268 – 215 =) 53 g; (Accept answers in range 51–57 g)
Units required, no workings required.
2
(d) (promotes) highest rate of growth at start of study / tapering off later in
the study;
Bt maize appears to cause less growth/mass gain than rat
food / vice versa;
more pronounced difference in females;
no difference in growth/mass gain between Bt and non-Bt maize;
2 max
(e) (Bt) maize may not be as good as the (commercially prepared) rat food;
Bt maize appears to be as good a food source as non-Bt maize;
Bt maize an acceptable/safe food source;
Answers require a judgement about Bt maize as a food source rather
than a description. 1 max
(f) decomposers / recycle nutrients / cause decay / nitrification/nitrogen
fixation / denitrification
1
(g) (for both groups) overall biomasses were higher during flowering than
harvest / vice versa
the microbial biomass for the Bt crop was (slightly) lower than for the
non-Bt crops at flower time;
the microbial biomass for the Bt crop was (slightly) higher than for
the non-Bt crops at harvest time; 2 max
(h) data does not support the hypothesis as there is little difference between
biomass found in the soil (surrounding) roots (of the Bt and non-Bt) at
either time;
data does not support the hypothesis as there is a slightly positive effect
at harvest;
data supports hypothesis as there is a slightly negative effect at flowering; 2 max
(i)
(i)
α helix / alpha helix
1
(ii) hydrogen bonds;
between the turns of the helix (rather than between R-groups);
bonds between carboxyl and NH groups/C-O---H-N; 2 max
(iii) non-polar amino acids/R-groups;
(inner part of phospholipid) bilayer is hydrophobic/non-polar; 2
[20]
5.
C
[1]
6.
D
[1]
7.
C
[1]